1. Field of the Invention
The present invention relates to treated metal oxide particles as well as to toner compositions including such treated metal oxide particles.
2. Description of the Related Art
Electrophotographic image formation includes developing an electrostatic latent image formed on a photoreceptor with a toner composition including a colorant dispersed in a binder resin, transferring the toner image to receiving paper, and fixing the transferred toner image by means of, for example, a hot roll. The photoreceptor is cleaned after the transferring step to prepare for the next latent image formation.
Treated metal oxide particles are commonly used in toner compositions as well as numerous other applications. In such toner applications, hydrophobicity imparting treating agents, including hydrocarbon chain silanes and/or siloxanes, are often utilized to render the metal oxide particles hydrophobic. The treated metal oxide particles are combined with toner particles in a toner composition in order to improve selected properties of the toner particles, including fluidity, transferability, fixability, and cleaning properties. In addition, the metal oxide particles are known to strongly influence the chargeability, i.e., tribocharge, of the toner composition.
The tribocharge of a toner composition containing metal oxide particles (particularly silica) depends on the temperature and relative humidity of the ambient environment. Often the tribocharge of toner formulated with silica particles is high at low humidity conditions and low at high humidity conditions. Such a dependence of the tribochargeability on environmental conditions leads to impaired transferability of the image and ultimately to reduced image quality. In contrast, the tribocharging of toner formulated with aluminum oxide particles is often too low under both high and low humidity conditions. While the chemical treatment utilized to render the metal oxide particles hydrophobic affects the tribocharge of the toner and tends to somewhat improve humidity sensitivity, there is a need for further improvement, particularly for toners formulated with silica.
Thus, a need exists for treated metal oxide particles that provide for toner compositions having improved humidity resistance in particular and reduced dependence on environmental conditions in general. There also exists a need for treated metal oxide particles facilitate fine-tuning the tribocharge of a toner composition within a wide range of tribocharge absolute values.